It depends on the game, really. If I'm playing a grind-heavy game, I'll try to make an equation of what monsters distribute how much exp in a certain area, then calculate how many monsters I'd need to kill in a certain time frame. Then I'll set a time frame to fight and level-up throughout the day, hoping to hit a certain level.
If the game is more quest oriented, I'll just follow my quest log.
Then there's certain games I set aside for irl 2-player, like Borderlands 2. Those days I'll see if I can get my friend to come over for the day, buy some snacks, order pizza, sit around and game together for the day.